Associations of El Nino/La Nina Southern Oscillation (ENSO) and Indian Ocean
Dipole (IOD) with local seasonal rainfall
Canonical correlation analysis was done between 1980-to-2011 monthly rainfall anomalies
and a set of ENSO and DMI indices for different month lags. Patterns of canonical variables
for the month lag yielding the highest canonical correlation are shown in Table 2 and
corresponding spatial distribution of canonical correlation coefficients are shown in Figure 4.
Monthly rainfalls show small anomalies (-15.7 to 113.7 mm, in Table 3) for mainland stations
during December to February (DJF), local dry season. For southern east coast stations,
December is not dry and the anomaly in DJF was high (-351 to 795 mm). This high anomaly
correlated to strong ENSO and IOD events occurring in previous two month (October to
December, OND), as suggested by high canonical correlation coefficient (r = 0.31 to 0.48)
over the South (see Figure 4 DJF). From Table 2, positive Indian Ocean Dipole and negative
Southern Oscillation Index (SOI), indicating El Nino, occurring in OND was likely found
with negative DJF rainfall anomaly over the southern east coast. Also, La Nino event in OND
was with more DJF rainfall. Moreover from Table 2, both ENSO and IOD strengths in OND
was equally associated with Thailand rainfall; whereas ENSO was dominant from January to
May and IOD was singly dominant in summer monsoon month (June to August, JJA). This
ENSO-IOD coexistence is consistent with the finding from the study on dipole variability of
sea surface temperature (SST) in the Indian Ocean, conducted by Baquero-Bernal et al.
(2002). They show that in most cases, El Nino and La Nina respond to basin-wide warm and
cold SST anomalies, respectively, in the Indian Ocean; but for September to November, the
ENSO events is primarily associated with dipole-like variability in the SST (Baquero-Bernal
et al., 2002). Our finding agrees this finding and shows further association of this ENSO-IOD
co-effect on rainfall anomaly in DJF over southern east coast of Thailand.